Backend & REST

// 1. Import Express and create the app instance
const express = require('express');
const app = express();
const PORT = 3000;

// 2. Middleware — tells Express to parse incoming JSON request bodies
//    Without this, req.body will be undefined on POST and PUT requests
app.use(express.json());

// 3. In-memory data store — simulates a database using a plain array
//    In a real app you would replace this with actual database calls
let users = [
  { id: 1, name: 'Alice', email: '[email protected]' },
  { id: 2, name: 'Bob',   email: '[email protected]'   },
];
let nextId = 3; // tracks the next available ID

// ── GET /api/users ─────────────────────────────────────────────
// Returns the full list of users as JSON
app.get('/api/users', (req, res) => {
  res.json({ success: true, data: users });
});

// ── GET /api/users/:id ──────────────────────────────────────────
// :id is a URL parameter — /api/users/2 gives req.params.id = "2"
app.get('/api/users/:id', (req, res) => {
  const user = users.find(u => u.id === parseInt(req.params.id));
  if (!user) return res.status(404).json({ success: false, message: 'User not found' });
  res.json({ success: true, data: user });
});

// ── POST /api/users ─────────────────────────────────────────────
// req.body contains the JSON you sent in the request body
app.post('/api/users', (req, res) => {
  const { name, email } = req.body;
  if (!name || !email) {
    return res.status(400).json({ success: false, message: 'Name and email are required' });
  }
  const newUser = { id: nextId++, name, email };
  users.push(newUser);
  res.status(201).json({ success: true, data: newUser });
});

// ── PUT /api/users/:id ──────────────────────────────────────────
// Replaces the entire user object (preserving the original ID)
app.put('/api/users/:id', (req, res) => {
  const index = users.findIndex(u => u.id === parseInt(req.params.id));
  if (index === -1) return res.status(404).json({ success: false, message: 'User not found' });
  users[index] = { id: users[index].id, ...req.body };
  res.json({ success: true, data: users[index] });
});

// ── DELETE /api/users/:id ───────────────────────────────────────
// Filters out the user with the matching ID from the array
app.delete('/api/users/:id', (req, res) => {
  const before = users.length;
  users = users.filter(u => u.id !== parseInt(req.params.id));
  if (users.length === before) return res.status(404).json({ success: false, message: 'User not found' });
  res.json({ success: true, message: 'User deleted' });
});

// 4. Start listening for incoming requests on PORT 3000
app.listen(PORT, () => {
  console.log(`Server running at http://localhost:${PORT}`);
});